1. Field of the Invention
The present invention relates to an optical pulse code recognition device and an optical distributor for recognizing all or a portion (for example, header code in packet signals) of optical pulse signals transmitted in optical communication systems.
2. Description of the Related Art
In recent years, an even higher rate of speed is being demanded in data communications in network systems such as on the Internet. This situation has increased the demand for ultra-high speed optical communication systems at rates to 1 Tb/s (1 terabit per second equals to 1012 bits per second). Possible transmission methods for ultra-high speed optical communication systems at the 1 Tb/s rate are wavelength-division multiplexing, time-division multiplexing and packet signal transmission.
The wavelength-division multiplexing method multiplexes the signal light on multiple channels having bit rates of 10 to 40 Gbps (1 gigabit per second equals to 109 bits per second) by slightly shifting each wavelength and sending it along an optical fiber transmission path, and this signal light is then distributed into multiple channels at the receiver and read out. In this method, the signals prior to multiplexing and after distributing are packet signals.
The time-division multiplexing method multiplexes the signal light of multiple channels having bit rates of 10 to 40 Gbps into a serial signal light along a time axis and sends it along an optical fiber transmission path, and the signal light is then distributed into multiple channels at the receiver and read out. In this method also, the signals prior to multiplexing and after distributing are packet signals. This method has the advantage that the signals can be electronically controlled before multiplexing and after distributing. However, the channel timing must be controlled during multiplexing and distributing.
In contrast, the packet transmission method, namely, the method for transmitting terabit signals (terabit order signals) as packets, can process signals for each packet so that the transmitting and receiving logic is simplified.
When receiving and distributing packet signals, the destination of each packet signal must be recognized and assigned to a transmission path to the destination. Each packet signal therefore is made up of a header (header code) containing address information on the destination, and a packet signal unit (payload) which is information to be sent.
In order to recognize a header code in the prior art, the header code is converted into an electrical code and then electronically recognized.
However, the current upper limit of electronic processing speed is 10 Gbps or 40 Gbps, and the higher bit-rate signals of 100 Gbps or 1 Tbps cannot be processed. Even assuming electronic processing is possible, multi-stage processing would be required so that the header recognition circuit design would be more complex in order to electronically recognize the header code, and the recognition would be delayed.
To resolve this problem, technology is disclosed in Japanese Patent Application No. 2000-245702 for processing and recognizing the header code contained in the packet signal optically. In this technology, the header code is processed as an optical signal, and the header light pulses are compared with the address code bit by bit.
However, the technology disclosed in Japanese Patent Application No. 2000-245702 has a problem that the header light pulses and the address code are compared bit by bit so that a large number of optical logic circuits are required, making the circuit design complex, and collective processing and recognition cannot be performed.